Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $231.87   13.163%   $262.391   $262.39   $262.40   $262.40  
  Purchase #2 $67.58   5.133%   $71.0489   $71.05   $71.05   $71.00  
  Purchase #3 $30.60   13.540%   $34.7432   $34.74   $34.75   $34.70  
  Purchase #4 $216.65   10.276%   $238.913   $238.91   $238.90   $238.90  
  Purchase #5 $39.36   5.818%   $41.65   $41.65   $41.65   $41.70  
  Purchase #6 $68.93   4.813%   $72.2476   $72.25   $72.25   $72.20  
  Purchase #7 $201.34   8.103%   $217.6546   $217.65   $217.65   $217.70  
  7 purchase totals = $856.33       $938.6483   $938.64   $938.65   $938.60